import { describe, it, expect, afterEach, vi } from 'vitest'
import {
  formatDateForDisplay,
  formatDateForInput,
  formatDateLocalISO,
  parseInputDate,
  isValidDate,
  getDayName,
  getMonthName,
  getISOWeekNumber,
  formatHolidayName,
  datesInRange,
} from '@/utils/dates'

describe('dates.ts utilities', () => {
  describe('formatDateForDisplay', () => {
    it('formats ISO string to Swedish display format', () => {
      const result = formatDateForDisplay('2026-06-15')
      expect(result).toBe('15 juni 2026')
    })

    it('formats Date object to Swedish display format', () => {
      const date = new Date('2026-06-15T00:00:00Z')
      const result = formatDateForDisplay(date)
      expect(result).toBe('15 juni 2026')
    })

    it('handles January correctly', () => {
      const result = formatDateForDisplay('2026-01-01')
      expect(result).toBe('1 januari 2026')
    })

    it('handles December correctly', () => {
      const result = formatDateForDisplay('2026-12-25')
      expect(result).toBe('25 december 2026')
    })

    it('returns empty string for invalid date', () => {
      const result = formatDateForDisplay('invalid')
      expect(result).toBe('')
    })

    it('defaults to Swedish when no locale is passed', () => {
      expect(formatDateForDisplay('2026-06-15')).toBe(formatDateForDisplay('2026-06-15', 'sv'))
    })

    it('formats in English when the "en" locale is passed', () => {
      const result = formatDateForDisplay('2026-06-15', 'en')
      expect(result).toBe('June 15, 2026')
    })

    it('formats in Swedish when the "sv" locale is explicitly passed', () => {
      const result = formatDateForDisplay('2026-06-15', 'sv')
      expect(result).toBe('15 juni 2026')
    })

    it('returns empty string for invalid date in the "en" locale too', () => {
      expect(formatDateForDisplay('invalid', 'en')).toBe('')
    })
  })

  describe('formatDateForInput', () => {
    it('formats ISO string to input format', () => {
      const result = formatDateForInput('2026-06-15')
      expect(result).toBe('2026-06-15')
    })

    it('formats Date object to input format', () => {
      const date = new Date('2026-06-15T00:00:00Z')
      const result = formatDateForInput(date)
      expect(result).toBe('2026-06-15')
    })

    it('pads month and day with zeros', () => {
      const result = formatDateForInput('2026-01-05')
      expect(result).toBe('2026-01-05')
    })

    it('returns empty string for invalid date', () => {
      const result = formatDateForInput('invalid')
      expect(result).toBe('')
    })
  })

  describe('formatDateLocalISO', () => {
    afterEach(() => {
      vi.unstubAllEnvs()
    })

    it('formats a Date built from local year/month/day components', () => {
      const date = new Date(2026, 5, 15) // local June 15, 2026
      expect(formatDateLocalISO(date)).toBe('2026-06-15')
    })

    it('pads single-digit month and day', () => {
      const date = new Date(2026, 0, 5) // local January 5, 2026
      expect(formatDateLocalISO(date)).toBe('2026-01-05')
    })

    it('reads the local calendar date, not the UTC one — this is the whole point of the function', () => {
      // Pacific/Kiritimati is UTC+14. A moment at 23:30 UTC on Jan 1 is
      // already local Jan 2 there. `formatDateForInput` (UTC getters) must
      // report Jan 1; `formatDateLocalISO` (local getters) must report
      // Jan 2. If this ever collapses to the same value, someone has
      // swapped in the UTC variant and reintroduced the off-by-one-day bug
      // this function exists to avoid.
      vi.stubEnv('TZ', 'Pacific/Kiritimati')
      const date = new Date(Date.UTC(2026, 0, 1, 23, 30))
      expect(formatDateForInput(date)).toBe('2026-01-01')
      expect(formatDateLocalISO(date)).toBe('2026-01-02')
    })
  })

  describe('parseInputDate', () => {
    it('parses ISO date string to Date object', () => {
      const result = parseInputDate('2026-06-15')
      expect(result).toBeInstanceOf(Date)
      expect(result.toISOString()).toContain('2026-06-15')
    })

    it('creates valid Date for valid input', () => {
      const result = parseInputDate('2026-06-15')
      expect(isValidDate(result)).toBe(true)
    })
  })

  describe('isValidDate', () => {
    it('returns true for valid Date object', () => {
      const date = new Date('2026-06-15')
      expect(isValidDate(date)).toBe(true)
    })

    it('returns false for invalid Date', () => {
      const date = new Date('invalid')
      expect(isValidDate(date)).toBe(false)
    })

    it('returns false for non-Date values', () => {
      expect(isValidDate('2026-06-15')).toBe(false)
      expect(isValidDate(20260615)).toBe(false)
      expect(isValidDate(null)).toBe(false)
      expect(isValidDate(undefined)).toBe(false)
    })
  })

  describe('getDayName', () => {
    it('returns Swedish day name', () => {
      const date = new Date('2026-06-15T00:00:00Z') // Monday
      const result = getDayName(date)
      expect(result.toLowerCase()).toBe('måndag')
    })

    it('returns empty string for invalid date', () => {
      const result = getDayName(new Date('invalid'))
      expect(result).toBe('')
    })
  })

  describe('getMonthName', () => {
    it('returns Swedish month name', () => {
      const date = new Date('2026-06-15T00:00:00Z')
      const result = getMonthName(date)
      expect(result).toBe('juni')
    })

    it('returns correct month names for all months', () => {
      const monthNames = [
        'januari',
        'februari',
        'mars',
        'april',
        'maj',
        'juni',
        'juli',
        'augusti',
        'september',
        'oktober',
        'november',
        'december',
      ]

      monthNames.forEach((monthName, index) => {
        const date = new Date(`2026-${String(index + 1).padStart(2, '0')}-15T00:00:00Z`)
        const result = getMonthName(date)
        expect(result).toBe(monthName)
      })
    })

    it('returns empty string for invalid date', () => {
      const result = getMonthName(new Date('invalid'))
      expect(result).toBe('')
    })
  })

  describe('getISOWeekNumber', () => {
    it('returns 0 for an invalid date', () => {
      expect(getISOWeekNumber(new Date('invalid'))).toBe(0)
    })

    it('computes the ISO week number for a mid-week date', () => {
      // 2026-06-15 is a Monday.
      expect(getISOWeekNumber(new Date('2026-06-15T00:00:00Z'))).toBe(25)
    })

    it('handles a Sunday correctly (getUTCDay() === 0 falls back to ISO day 7)', () => {
      // 2026-01-11 is a Sunday, closing out ISO week 2 of 2026.
      expect(getISOWeekNumber(new Date('2026-01-11T00:00:00Z'))).toBe(2)
    })
  })

  describe('formatHolidayName', () => {
    it('returns the name unchanged when it has no ";" segments', () => {
      expect(formatHolidayName('Midsommardagen')).toBe('Midsommardagen')
    })

    it('strips a trailing weekday segment', () => {
      expect(formatHolidayName('Påskdagen; Söndag')).toBe('Påskdagen')
    })

    it('falls back to the first segment when every segment is a weekday name', () => {
      // Contrived input where nothing survives the weekday filter — the
      // function must not return an empty string in that case.
      expect(formatHolidayName('Söndag; Måndag')).toBe('Söndag')
    })
  })

  describe('datesInRange', () => {
    it('returns an empty array when the start date is invalid', () => {
      expect(datesInRange('invalid', '2026-06-15')).toEqual([])
    })

    it('returns an empty array when the end date is invalid', () => {
      expect(datesInRange('2026-06-15', 'invalid')).toEqual([])
    })

    it('returns the inclusive range in ascending order for start before end', () => {
      expect(datesInRange('2026-06-01', '2026-06-03')).toEqual([
        '2026-06-01',
        '2026-06-02',
        '2026-06-03',
      ])
    })

    it('returns the same range regardless of argument order (reversed input)', () => {
      expect(datesInRange('2026-06-03', '2026-06-01')).toEqual([
        '2026-06-01',
        '2026-06-02',
        '2026-06-03',
      ])
    })

    it('returns a single date when start equals end', () => {
      expect(datesInRange('2026-06-01', '2026-06-01')).toEqual(['2026-06-01'])
    })
  })
})